This is a randomized, controlled trial to compare supported treadmill ambulation training (STAT) to conventional gait training for improving gait speed, gait endurance, gait efficiency and muscle function in SCI subjects injured more than six months prior to start of training. Each subject will receive twelve weeks of either CGT or STAT, given as 20 minutes of training within a one-hour period per day, five days per week. These subjects will be studied baseline, 4,8 and 12 weeks of training, and three months after the end of training with a battery of tests designed to evaluate the subjects' gait and muscle function.